H8 CP/NET SPI WIZNET Network Card Overview

What is this card used for?

The H8 CP/NET SPI WIZNET Network Card is an Ethernet expansion board designed for the Heathkit H8 retro computer.

It uses the WIZnet WIZ850io module (based on the W5500 Ethernet controller) to provide TCP/IP networking over an SPI interface.

Its main purpose is to enable CP/NET networking on the H8, allowing the machine to act as a CP/NET client and connect to a CP/NET server. Through this, the H8 can support remote disk access, file transfers, and shared resources just like in the CP/M era.

Documentation includes schematics, GAL files, firmware, and CP/M3 disk images with network support, making it a practical project for builders and enthusiasts.

What is the Heathkit H8?

The Heathkit H8 was an Intel 8080A-based 8-bit microcomputer kit released in 1977.

It ran CP/M or Heath’s own HDOS operating system.

Unlike many contemporaries that used the S-100 bus, the H8 introduced its own 50-pin “Benton Harbor” bus, forming the basis of the H8/H89 family of systems.

Why WIZnet (W5500)?

The W5500 includes a built-in TCP/IP stack, which offloads protocol handling from the host CPU.

This makes it ideal for retro systems like the H8, where resources are limited but reliable Ethernet networking is desired.

The WIZ850io module integrates the W5500, transformer, and RJ-45 connector into a compact plug-in board, making it straightforward to connect via SPI.

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